Time domains synchronization in a system on chip

ABSTRACT

A method for synchronizing a first time domain with a second time domain of a system on chip includes a detection of at least one periodic trigger event generated in the first time domain, the second time domain or in a third time domain; acquisitions, made at the instants of the at least one trigger event, of the current timestamp values representative of the instantaneous states of the time domain(s) other than the trigger time domain; a comparison, made in the third time domain, between differential durations between current timestamp values which are respectively acquired successively; and a synchronization of the second time domain with the first time domain, on the basis of the comparison.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of French Application No. 2100697,filed on Jan. 26, 2021, which application is hereby incorporated hereinby reference.

TECHNICAL FIELD

Embodiments and implementations relate to systems on chip, and inparticular the synchronization of time domains in a system on chip.

BACKGROUND

In electronic devices comprising several microprocessors ormicrocontrollers, it is necessary to share a common vision of timebetween them.

A system on chip is usually designated as a system embedded in the sameintegrated circuit including a microprocessor or microcontroller andother devices, such as for example at least one communication interface.

The shared time can be a global time, that is to say an absolute timefor example resulting from a real date, or a local time, called networktime, not necessarily having an absolute reference but identical to allthe elements of a network.

The time information exchanged must be precise, for example of a levelbelow a microsecond, and synchronized, so that distributed processes canbe started simultaneously, such as for example a multi-axis motioncontrol for robotics.

The sharing of time information is done through a communicationinterface, such as a Peripheral Component Interconnect express “PCIe”interface, or a wired network interface usually called “Ethernet.” PCIeand Ethernet interfaces are well known to a person skilled in the art.

Communication interfaces are typically intended to operate underspecific communication protocols, and communication protocols mayprovide for specific time information sharing.

Consequently, each communication interface is typically adapted for aspecific time sharing protocol and this is referred to as “time domains”for the different visions of time obtained by the differentcommunication interfaces of a system on chip.

In particular, PCIe interfaces provide for sharing time informationaccording to a process called Precision Time Measurement (usually “PTM”)wherein a “master” device called Root Complex (usually “RC”) shares timeinformation of a common clock on which the “slave” devices called EndPoints (usually “EP”) are synchronized; and, the Ethernet interfacesprovide for sharing time information according to a process calledPrecision Time Protocol (usually “PTP”), to share a common clock betweenend points.

The shared time information can be coded differently depending on thecommunication protocol used, for example the PTM protocol can provide aclock encoded by a 64-bit binary word incremented at 250 MHz, while thePTP protocol can provide a digital value representative of thenanoseconds on 32 bits, and a digital value representative of theseconds on 32 bits.

Conventional techniques for sharing time information and synchronizingsystems on chip have difficulties insofar as the time domains used maybe disciplined by different protocols and not directly compatible witheach other, such as for example the PTM protocols of PCIe interfaces andthe PTP protocols of Ethernet interfaces.

Moreover, it is desirable not to introduce changes in the communicationinterfaces, since they typically have the need to be compatible withthird-party devices, as defined by standards or consensus.

There is therefore a need to be able to synchronize different timedomains in the same system on chip.

SUMMARY

According to one aspect, provision is made of a method for synchronizinga first time domain of a first device with a second time domain of asecond device. The method comprises a detection of at least one periodictrigger event generated in at least one trigger time domain selectedfrom the first time domain, the second time domain and a third timedomain of a third device. The method comprises acquisitions, made at theinstants of detection of the at least one trigger event, of the currenttimestamp values representative of the instantaneous states of the firsttime domain, of the second time domain and of the third time domainother than the at least one trigger time domain. The method comprises acomparison, made in the third time domain, between differentialdurations between current timestamp values which are respectivelyacquired successively. The method comprises a synchronization of thesecond time domain with the first time domain, on the basis of thecomparison.

In other words, the method according to this aspect uses the third timedomain as an intermediary in order to measure a possible shift in thelapse of time between the point of vision of the first time domain andthe point of vision of the second time domain, which are potentially notdirectly comparable with each other.

Indeed, the comparison of the elapsed time between two timestamp valuesof a time domain with the elapsed duration in the third time domainbetween two trigger events, or with the elapsed duration between twotimestamp values of at least one other time domain, allows havinginformation on the difference in the speed of lapse of time between thetwo considered domains, that is to say between the time domain providingthe timestamp value and the time domain providing the trigger events, orbetween the two time domains providing timestamp values at the instantsdefined by the trigger events.

Furthermore, the method according to this aspect does not introduce anyfunctional or structural modification to the elements of the first timedomain or of the second time domain, but advantageously uses timestampinformation usually provided to synchronize the time domains, from thethird-party third time domain.

For example, the acquisitions of the current timestamp values can bemade at the same instants of detection of the same periodic triggerevent, or at different instants of detection of various periodic triggerevents.

According to one implementation, the first time domain is defined by aprecision time measurement protocol “PTM” of a peripheral componentinterconnect express “PCIe” interface, the second time domain is definedby a precision time protocol “PTP” of a network interface “Ethernet,”and the third time domain is clocked by a free running local clockadapted for software operations.

Indeed, a problem exists in particular in conventional systems on chipusing both a time domain defined by PTM, and a time domain defined byPTP, given that the PCIe and Ethernet interfaces are typically used andconsequently very widespread.

This implementation thus allows resolving this particular andconventionally very widespread problem.

According to one implementation, the at least one trigger time domaincomprises the first time domain, and the at least one trigger eventgenerated in the first time domain occurs when a condition is verifiedon a transition of at least one bit of a current timestamp valuerepresentative of the instantaneous state of the first time domain, eachbit of the current timestamp value being communicated on a dedicatedchannel of a timestamp bus.

On the one hand, the trigger events can be conditioned by a combinationof bits of the timestamp bus, which allows constructing “complex”trigger events having a periodicity which is not available in thesignals passing through the timestamp bus as such. This can for exampleallow constructing an optimized period for a particular processing inthe third time domain.

On the other hand, it should be noted that the communication of each bitof the current timestamp value on a dedicated channel of a timestamp busis used in particular by PCIe interfaces using the PTM.

According to one implementation, the at least one trigger time domaindoes not comprise the first time domain, each bit of the currenttimestamp value representative of the instantaneous state of the firsttime domain is communicated on a dedicated channel of a timestamp bus,and the acquisition of the current value representative of theinstantaneous state of the first time domain comprises a loading of alatch with the bits present on each channel of the timestamp bus, theloading of the latch being controlled at the instants of detection ofthe at least one periodic trigger event.

Here again, it will be noted that the communication of each bit of thecurrent timestamp value on a dedicated channel of a timestamp bus isused in particular by the PCIe interfaces using the PTM, and thisimplementation allows simply retrieving the current timestamp value ofthe first time domain, without modifying the structure or the operationof the first time domain.

According to one implementation, the at least one trigger time domaincomprises the second time domain, and the at least one trigger eventgenerated in the second time domain is detected when a periodic signalis generated in the second time domain.

Thus, in the case where the at least one time domain comprises both thefirst time domain and the second time domain, the method comprisesacquisitions of first current timestamp values and respectively ofsecond current timestamp values representative of the instantaneousstates of the third time domain, made at the instants of detection ofthe first trigger events originating from the first time domain andrespectively at the instants of detection of the second trigger eventoriginating from the second time domain. The comparison is made betweenthe differential durations between the first current timestamp values,and the differential durations between the second current timestampvalues.

And, in the case where the at least one second time domain comprisesonly the second time domain, the method comprises acquisitions ofcurrent timestamp values representative of the instantaneous states ofthe first time domain as well as acquisitions of current timestampvalues representative of the instantaneous states of the third timedomain, at the instants of detection of the second trigger eventsoriginating from the second time domain. The comparison is made betweenthe differential durations between the respective current timestampvalues.

According to another aspect, provision is made of a system, for exampleincorporated in an integrated manner in a system on chip, including afirst device comprising a first counter configured to have a currenttimestamp value representative of the instantaneous state of a firsttime domain, a second device comprising a second counter configured tohave a current timestamp value representative of the instantaneous stateof a second time domain, and a third device comprising a local clockgenerator configured to clock a third time domain. The third deviceincludes a synchronization module configured to detect at least oneperiodic trigger event generated in at least one trigger time domainselected from the first time domain, the second time domain and thethird time domain. The synchronization module is configured to acquire,at the instants of detection of the at least one trigger event, thecurrent timestamp values representative of the first time domain, of thesecond time domain and of the third time domain other than the at leastone trigger time domain. The synchronization module is configured tocompare differential durations between current timestamp values whichare respectively acquired successively. The synchronization module isconfigured to generate a control adapted for synchronizing the secondtime domain with the first time domain, on the basis of the comparison.

The synchronization module can be configured to acquire the currenttimestamp values at the same instants of detection of the same triggerevent, or at different instants of detection of different triggerevents.

According to one embodiment, the first device comprises a peripheralcomponent interconnect express “PCIe” interface configured to define thefirst time domain by a precision time measurement “PTM” protocol, thesecond device comprises a network interface “Ethernet” configured todefine the second time domain by a precision time protocol “PTP,” andthe local clock generator of the third device is adapted to clocksoftware operations.

According to one embodiment, the at least one trigger time domaincomprises the first time domain, the first counter is configured tocommunicate each bit of the current timestamp value on a dedicatedchannel of a timestamp bus, and the synchronization module is configuredto detect the at least one trigger event generated in the first timedomain, when a condition is verified on a transition of at least one biton the respective channel(s) of the timestamp bus.

According to one embodiment, the at least one trigger time domain doesnot comprise the first time domain, the first counter is configured tocommunicate each bit of the current timestamp value on a dedicatedchannel of a timestamp bus, and the synchronization module includes alatch on the timestamp bus and is configured to acquire the currentvalue representative of the instantaneous state of the first time domainby controlling a loading of the latch, at the instant of the at leastone trigger event, with the bits present on each channel of thetimestamp bus.

According to one embodiment, the at least one trigger time domaincomprises the second time domain (optionally in addition to the firsttime domain), and the synchronization module is configured to detect theat least one trigger event generated in the second time domain, when aperiodic signal is generated in the second time domain.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and features of the invention will become apparent uponexamining the detailed description of implementations and embodiments,which are in no way limiting, and the appended drawings, wherein:

FIG. 1A illustrates a first alternative of an SoC system;

FIG. 1B illustrates a second alternative of an SoC system;

FIG. 1C illustrates a third alternative of an SoC system;

FIG. 1D illustrates a fourth alternative of an SoC system;

FIG. 2 illustrates an embodiment system on chip;

FIG. 3 is a graph illustrating a lapse of time in the first time domaincompared to a lapse of time in the third time; and

FIG. 4 illustrates an embodiment system on chip.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

FIGS. 1A, 1B, 1C and 1D illustrate four possible alternatives of an SoCsystem including a first device DIS1 comprising a first counter TMR1configured to have a current timestamp value representative of theinstantaneous state of a first time domain DMN1; a second device DIS2comprising a second counter TMR2 configured to have a current timestampvalue representative of the instantaneous state of a second time domainDMN2; a third device DIS3 comprising a third counter TMR3 configured tohave a current timestamp value representative of the instantaneous stateof a third time domain DMN3, and synchronization module MSYNC configuredto synchronize SYNC the second time domain DMN2 on the first time domainDMN1.

The system SoC can be integrated in the same integrated circuit, usuallycalled in this case “system on chip,” or in systems on chips which aredifferent and interconnected by wire links, each including at least oneof the first, second and third device DIS1, DIS2, DIS3.

In the following, the non-limiting example where the three devices DIS1,DIS2, DIS3 and the respective time domains DMN1, DMN2, DMN3, belong tothe same system on chip SoC will be considered.

Current timestamp values are digital representations of an instantaneoustime, that is to say, “a date” in the broad sense. In the system on chipSoC, the different timestamp “dates” used can have an amplitude (that isto say maximum value) of a great number of years (hundred(s) of years)and precision (that is to say minimum variation) of the order of ananosecond or even less.

Each time domain DMN1, DMN2, DMN3 is clocked by a respective local clocksignal generator clk1, clk2, clk3. The local clock signal generatorsclk1, clk2, clk3 can be produced in the form of local oscillators, suchas for example usually crystal oscillators (for example quartz) with aphase locked loop, and optionally compensated in temperature; but also,other types of oscillators, less common in the field of clockgeneration, such as variable frequency oscillators, voltage controlledoscillators, phase locked loops, or else analogue or digital frequencysynthesizers.

According to a particular and non-limiting example, the third deviceDIS3 can comprise or constitute a microprocessor or a microcontroller,that is to say more broadly a calculation unit adapted for implementingsoftware operations, and the local clock generator clk3 of the thirddevice DIS3 is in particular intended to clock the software operations.

The synchronization module MSYNC can be implemented by hardwarebelonging to the third device DIS3, or by software implemented in thethird device DIS3.

In the representations of FIGS. 1A, 1B, 1C and 1D, the local clockgenerators clk1, clk2, clk3 integrate the respective devices DIS1, DIS2,DIS3, but could come from sources which are external but belonging tothe respective time domains DMN1, DMN2, DMN3.

According to a particular and non-limiting example (see below inrelation to FIGS. 2 to 4 ), the first device DIS1 can comprise orconstitute a peripheral component interconnect express “PCIe” interface,and the specifications of which, well known to a person skilled in theart, are managed and developed by the PCI-SIG (“PCI Special InterestGroup”) consortium.

According to a particular and non-limiting example (described below inrelation to FIGS. 2 to 4 ), the second device DIS2 may comprise orconstitute a wired physical network interface “Ethernet,” for example asdefined by the standard IEEE802.3 and its variants, well known to aperson skilled in the art.

However, the first device DIS1 and the second device DIS2 may compriseor constitute other technologies (typically communication interfaces)adapted to exchange time information in order to synchronize distincttime domains, such as in particular the CAN (for “Controller AreaNetwork”) interfaces and the FDCAN (for “Flexible Data CAN”) or TTCAN(for “Time Triggered CAN”) variants, but also 4G, 5G, LTE communicationswhich have synchronization possibilities of the order of themicrosecond.

FIG. 1A illustrates a first alternative of the configuration of thesynchronization module MSYNC, integrated in the third device DIS3, forsynchronizing SYNC the second time domain DMN2 on the first time domainDMN1 of the system on chip SoC.

In this first alternative, the synchronization module MSYNC isconfigured to detect a trigger event TRG generated periodically in thefirst time domain DMN1. The first time domain DMN1 is called in thisregard “trigger time domain.”

The duration of the period of the trigger event, considered in the firsttime domain DMN1, can be known by the synchronization module MSYNC byconstruction.

The synchronization module MSYNC is configured to acquire the currenttimestamp values TS2 representative of the instantaneous states of thesecond time domain DMN2, at the successive instants of detection of theperiodic trigger event TRG.

The synchronization module MSYNC is configured to compare a differentialduration between successive trigger events TRG with a differentialduration between current timestamp values TS2 which are respectivelyacquired successively.

“Differential duration” means the value of the difference between two ofthe considered measurements, that is to say the difference between thetimestamp values, or the time difference between trigger events.

The differential duration between successive trigger events TRG is forexample made with prior knowledge of their periodicity in the first timedomain DMN1, and/or by a measurement of the differential durationbetween current timestamp values TS31 of the third time domain DMN3acquired at the moments of detection of trigger events TRG originatingfrom the first time domain DMN1.

Indeed, on the one hand, the synchronization module MSYNC has acquiredinformation on the lapse of time in the first time domain DMN1 by theinstants of detection of the periodic trigger events TRG. Thus, thesynchronization module MSYNC can for example detect a slowing down ofthe lapse of time in the first time domain DMN1 if the period betweentwo detections of the trigger event TRG increases.

On the other hand, the synchronization module MSYNC has acquiredinformation on the lapse of time in the second time domain DMN2 by thecurrent timestamp values TS2. The difference between timestamp valuesTS2 indeed provide the duration elapsed between the correspondingtrigger events, this time considered in the second time domain DMN2.

Finally, the synchronization module MSYNC is configured to generate acontrol SYNC adapted for synchronizing the second time domain DMN2 withthe first time domain DMN1, on the basis of the comparison.

In particular, the control SYNC is adapted to adjust the frequency, andoptionally the phase, of the local clock signal generated by the localclock generator clk2 of the second time domain DMN2.

Indeed, from the information on the lapse of time in the first timedomain DMN1 and the information on the lapse of time in the second timedomain DMN2, the synchronization module MSYNC can calculate a correctionto be applied in the second time domain DMN2 so that it corresponds tothe first time domain DMN1.

For example, if the lapse of time in the first time domain DMN1 hasslowed down, the control SYNC may comprise a reduction in the frequencyof the clock generated by the local clock generator clk2 of the secondtime domain DMN2.

According to another example of synchronization, if the duration betweentwo trigger events TRG, obtained by the difference between the timestampvalues TS2 and therefore considered in the second time domain DMN2, isdifferent from the duration between the corresponding trigger eventsTRG, considered in the first time domain DMN1 with prior knowledge ofthe periodicity of the trigger events TRG or else considered in thethird time domain DMN3, the control SYNC can adjust the frequency of theclock clk2 of the second time domain DMN2, to equalize the measurementof time in the second time domain DMN2 to the measurement of time in thefirst time domain DMN1.

Indeed, the synchronization module MSYNC is capable of identifying alinear relationship (for example in “y=ax+b”) between the time (“y”) ofthe first time domain DMN1 and the time (“x”) of the second time domainDMN1. The control SYNC allows applying the proportional correction (“a”)and offset (“b”) parameters.

FIG. 1B illustrates a second alternative of the configuration of thesynchronization module MSYNC, integrated in the third device DIS3, forsynchronizing SYNC the second time domain DMN2 on the first time domainDMN1 of the system on chip SoC.

In this second alternative, the synchronization module MSYNC isconfigured to detect a trigger event TRG generated periodically in thesecond time domain DMN2. The second time domain DMN2 is called in thisregard “trigger time domain.”

The synchronization module MSYNC is configured to acquire the currenttimestamp values TS1 representative of the instantaneous states of thefirst time domain DMN1, at the successive instants of detection of theperiodic trigger event TRG.

The synchronization module MSYNC is configured to compare a differentialduration between successive trigger events TRG with a differentialduration between current timestamp values TS1 which are respectivelyacquired successively.

The differential duration between successive trigger events TRG is forexample made with prior knowledge of their periodicity in the secondtime domain DMN2, and/or by a measurement of the differential durationbetween current timestamp values TS32 of the third time domain DMN3acquired at the moments of detection of trigger events TRG from thesecond time domain DMN2.

Finally, the synchronization module MSYNC is configured to generate acontrol SYNC adapted for synchronizing the second time domain DMN2 withthe first time domain DMN1, on the basis of the comparison.

Here again, the synchronization module MSYNC has acquired informationrepresentative of the first time domain DMN1 and of the second timedomain DMN2. The differential durations calculated from this informationwill allow identifying a relationship between the lapse of time in thesecond time domain DMN2 compared to the lapse of time in the first timedomain DMN1, in order to set the control SYNC of synchronization of thesecond time domain DMN2.

FIG. 1C illustrates a third alternative of the configuration of thesynchronization module MSYNC, integrated in the third device DIS3, forsynchronizing SYNC the second time domain DMN2 on the first time domainDMN1 of the system on chip SoC.

In this third alternative, the synchronization module MSYNC isconfigured to detect a trigger event TRG generated periodically in thethird time domain DMN3. The third time domain DMN3 is called in thisregard “trigger time domain.”

For clarification of the use of the terms, given that thesynchronization module MSYNC is part of the third device DIS3 of thethird time domain DMN3, it could be considered that the synchronizationmodule MSYNC is configured to itself generate the periodic triggerevents TRG. However, strictly speaking, the trigger events TRG come froma time management mechanism TMR3 (usually “timer”) from the local clockclk3, and the trigger events TRG, as such, are not generated directly bythe synchronization module MSYNC. Thus, it is considered that thetrigger events TRG are generated by the third device DIS3, and that thesynchronization module MSYNC of the third device DIS3 is configured todetect the trigger events TRG.

The synchronization module MSYNC is configured to acquire the currenttimestamp values TS1 representative of the instantaneous states of thefirst time domain DMN1, at the successive instants of detection of theperiodic trigger event TRG, and to acquire the current timestamp valuesTS2 representative of the instantaneous states of the second time domainDMN2, at the successive instants of detection of the periodic triggerevent TRG.

It will be noted that the acquisitions TS1, TS2 can be made at the sameinstants of detection of the same periodic trigger event TRG, or atdifferent instants of detection of various periodic trigger events, inparticular, a trigger event can be respectively assigned to each of thefirst and second devices DIS1, DIS2.

The synchronization module MSYNC is configured to compare thedifferential duration between the current timestamp values TS1 of thefirst time domain DMN1 acquired successively, with the differentialduration between the current timestamp values TS2 of the second timedomain DMN2 acquired successively.

The comparison can further take into account the differential durationbetween the corresponding successive trigger events TRG, in particularin the case where several distinct trigger events are used.

Finally, the synchronization module MSYNC is configured to generate acontrol SYNC adapted for synchronizing the second time domain DMN2 withthe first time domain DMN1, on the basis of the comparison.

Here again, the synchronization module MSYNC has acquired informationrepresentative of the first time domain DMN1 and the second time domainDMN2 (that is to say the current timestamp values TS1, ST2). Thedifferential durations calculated from this information will allowidentifying a relationship between the lapse of time in the second timedomain DMN2 compared to the lapse of time in the first time domain DMN1,in order to set the control SYNC of synchronization of the second timedomain DMN2.

FIG. 1D illustrates a fourth alternative of the configuration of thesynchronization module MSYNC, integrated in the third device DIS3, forsynchronizing SYNC the second time domain DMN2 on the first time domainDMN1 of the system on chip SoC.

In this fourth alternative, the synchronization module MSYNC isconfigured to detect a first trigger event TRG10 generated periodicallyin the first time domain DMN1 and a second trigger event TRG20 generatedperiodically in the second time domain DMN2. The first and the secondtime domains DMN1, DMN2 are called in this regard “trigger timedomains.”

The synchronization module MSYNC is configured to acquire the firstcurrent TS31 timestamp values representative of the instantaneous statesof the third time domain DMN3, at the successive instants of detectionof the first periodic trigger event TRG10.

Similarly, the synchronization module MSYNC is configured to acquiresecond current timestamp values TS32 representative of the instantaneousstates of the third time domain DMN3, at the successive instants ofdetection of the second periodic trigger event TRG20.

The synchronization module MSYNC is configured to compare thedifferential durations between the first current timestamp values TS31which are respectively acquired successively, with the differentialdurations between the second current timestamp values TS32 which arerespectively acquired successively.

Finally, the synchronization module MSYNC is configured to generate acontrol SYNC adapted for synchronizing the second time domain DMN2 withthe first time domain DMN1, on the basis of the comparison.

Here again, the synchronization module MSYNC has acquired informationrepresentative of the first time domain DMN1 and of the second timedomain DMN2, from the point of vision of the third time domain DMN3. Thedifferential durations calculated from this information will allowidentifying a relationship between the lapse of time in the second timedomain DMN2 compared to the lapse of time in the first time domain DMN1,in order to set the control SYNC of synchronization of the second timedomain DMN2.

FIG. 2 illustrates a particular exemplary embodiment of the system onchip SoC, wherein the first device DIS1 is of the peripheral componentinterconnect express “PCIe” interface type, and wherein the seconddevice DIS2 is of the wired network interface type “Ethernet.”

The third device DIS3 is a calculation unit of the microprocessor ormicrocontroller central processing unit “CPU” type, including thesynchronization module MSYNC produced in hardware or software form. Thethird time domain is a software application time domain APP (DMN3).

The PCIE interface (DIS1) is configured to share time informationrelating to the first time domain DMN1 by a precision time measurement“PTM” protocol.

In this context, the local clock pipe_clk (clk1) can for example have afrequency of 250 MHz (megaHertz), that is to say a period of 4 ns(nanoseconds), and the first counter PTM_CNT (TMR1) provides a 64-bitbinary word, incremented by the timing of the local clock pipe_clk at250 MHz. Consequently, the digital value of the first counter PTM_CNT(TMR1) corresponds to a time value in units of 4 ns.

In the PTM protocol, sharing time information is made by communicatingeach of the 64 bits of the current timestamp value PNT_CNT (TMR1) on arespectively dedicated channel of a timestamp bus PTM_BUS_64 bit.Consequently, the bus PTM_BUS_64 bit is at a constantly updatedtimestamp value.

Moreover, the first counter PTM_CNT (TMR1) is capable of receiving andemitting a synchronization update control updt, between various devicesusing the PTM protocol.

The Ethernet interface ETH (DIS2) is configured to share timeinformation relating to the second time domain DMN2 by a Precision TimeProtocol “PTP.”

In this context, the local clock ptp_clk (c1 k 2) can for example have afrequency comprised between 125 MHz and 200 MHz, and the second counterPTP_CNT (TMR2) can comprise two 32-bit binary words, one encoding theseconds of the timestamp value (32 bit s), and the other encoding thenanoseconds of the timestamp value (32 bit ns).

In the PTP protocol, the sharing of time information can be done viaregisters of the Ethernet interface ETH (DIS2), storing a timestampvalue TS2, and which are read by the synchronization module MSYNC. Asignal usually called a pulse per second “PPS,” but which is notnecessarily limited to one pulse per second, can be configured totrigger a reading by the synchronization module MSYNC in the registersof the Ethernet interface ETH (DIS2) at desired instants.

Thus, in this example where the trigger time domain comprises the firsttime domain PTM (DMN1), that is to say according to the alternativesdescribed above in relation to FIG. 1A or 1D, at least one periodictrigger event TRG1, TRG2 is generated by the first counter PTM_CNT(TMR1).

Advantageously taking advantage of the already existing construction ofthe bus PTM_BUS_64 bit in the PCIe interfaces, the periodic triggerevents TRG1, TRG2 are defined by a transition (that is to say a risingedge or a falling edge) of at least one signal on the channels of thebus PTM_BUS_64 bit.

Indeed, the least significant bit of the bus PTM_BUS_64 bit constitutesa periodic signal with a period of 4ns, and in particular the bit ofweight 17 (bit17) constitutes a periodic signal with a period close to 1ms and the bit of weight 20 (bit20) constitutes a periodic signal with aperiod close to 8 ms, by the mechanism for incrementing the binary wordof the first counter PTM_CNT (TMR1).

And, in this example, two separate trigger events TRG1, TRG2 are used,the first trigger event TRG1 occurring during a rising edge on the bit17, and the second trigger event TRG2 occurring during a rising edge onthe bit 20.

Furthermore, in an example not shown, each trigger event can beconstructed by a logical condition on a transition of several bits ofthe current timestamp value distributed on the bus PTM_BUS_64 bit. Thisallows constructing “complex” trigger events having a periodicity whichis not available in the signals passing over the timestamp busPTM_BUS_64 bit as such. For example, a period close to 1.5 ms is notdirectly available on the bus PTM_BUS_64 bit, but can be roughlyconstructed by checking an “AND” condition on the rising edges of bit 17and bit 16.

In the example shown, the two trigger events TRG1, TRG2 are detected bythe synchronization module MSYNC, but only the second trigger event TRG2(bit20) controls an acquisition of the PPS current timestamp value (TS2)representative of the instantaneous state of the second PTP time domain(DMN2).

Reference is made in this regard to FIG. 3 .

FIG. 3 is a graph showing the lapse of time in the first time domainDMN1 on the y-axis PCIE_EP_t, compared to the lapse of time in the thirdtime domain APP (DMN3) on the x-axis TMR3_t.

The plateau in the lapse of time in the first time domain DMN1 shows anadjustment of the local clock pipe_clk (clk1) of the PCIe interface ofthe “End Point” EP type on an external clock of a PCIe interface of the“Root Complex” RC type.

The frequency of the external clock of the PCIe RC interface can varyfor various reasons, as shown by the dotted lines PCIE_RC_t1,corresponding to 249 MHz, then by the dotted lines PCIE_RC_t2,corresponding to 248 MHz, while the local clock pipe_clk remains stableat a frequency of 250 MHz.

The advance of time PCIE_EP_t in the time domain of the PCIe EPinterface relative to the time domain of the PCIe RC interface iscompensated by substantially “stopping” the clock pipe_clk (clk1) duringthe plateau.

Advantageously, the PTM synchronizations of the PCIe EP interface on thePCIe RC interface are controlled by the third device CPU, via the signalupdt (FIG. 2 ), after each first trigger events TRG1_1, TRG1_2, TRG1_3,TRG1_4.

Consequently, the slower the time domain of the PCIe RC interface, thegreater the differential duration t1, t2 between the trigger eventsTRG1_i, t2>t1.

At the same time, the synchronization module MSYNC reads the currenttimestamp values TS2_1, TS2_2 representative of the instantaneous statesof the second PTP time domain (DMN2) at the instants of detection of thesecond trigger events TRG2 (PPS).

The difference “TRG1_i+1−TRG1_i,” that is to say the durations t1, t2 inthe third time domain TMR3_t (DMN3), is used to discipline SYNC thelocal clock generator ptp_clk (c1 k 2) of the Ethernet interface ETH(DIS2) on the first PTM time domain (DMN1), by comparing it to thedifference “TS2_j+1−TS2_j” of the current timestamp values supplied bythe Ethernet interface ETH (DIS2).

In other words, a comparison is made in the third time domain, between adifferential duration between successive trigger events TRG1_i (with1≤i≤4 in FIG. 3 ), and a differential duration between current timestampvalues acquired successively PPS_j (with 1≤j≤2 in FIG. 3 ), in order tosynchronize the second time domain DMN2 with the first time domain DMN1.

FIG. 4 shows an advantageous exemplary embodiment for the alternativesof the system on chip SoC described previously in relation to FIGS. 1Band 1C, that is to say the alternatives wherein the trigger time domaindoes not comprise the first time domain.

In this example, the first device PCIE RC/EP (DIS1) is again of the PCIeinterface type, and the first counter PTM_CNT (TMR1) supplies a 64-bitbinary word on a 64-bit timestamp bus PTM_BUS_64 bit, as previouslydescribed in relation to FIG. 2 .

The synchronization module includes a 64-bit latch LTCH, on therespective channels of the timestamp bus PTM_BUS_64 bit, in order toacquire the current timestamp value Capt_64 bit (TS1) representative ofthe instantaneous state of the first time domain DMN1. A loading of thelatch with the bits present on each channel of the timestamp busPTM_BUS_64 bit is ordered at the instant of the at least one triggerevent TRG, that is to say for example by the trigger event TRG itself.

This allows in particular not modifying the operation of the interfacePCIe, whether of the EP or RC type, in particular with regard to theimplementations of the PTM protocol with any other PCIe device externalto the system on chip SoC.

What is claimed is:
 1. A method for synchronizing a first time domain ofa first device with a second time domain of a second device, the methodcomprising: detecting at least one periodic trigger event generated inat least one trigger time domain selected from the first time domain,the second time domain, and a third time domain of a third device;acquiring, at instants of detecting the at least one periodic triggerevent, current timestamp values representing instantaneous states of thefirst time domain, the second time domain, and the third time domain,other than the at least one trigger time domain; comparing, in the thirdtime domain, differential durations between the current timestamp valuesthat are respectively acquired successively; and synchronizing thesecond time domain with the first time domain based on the comparing. 2.The method according to claim 1, wherein acquiring the current timestampvalues is performed at same instants of detecting a same periodictrigger event, or at different instants of detecting different periodictrigger events.
 3. The method according to claim 1, wherein the firsttime domain is defined by a precision time measurement protocol “PTM” ofa peripheral component interconnect express “PCIe” interface, the secondtime domain is defined by a precision time protocol “PTP” of a networkinterface “Ethernet,” and the third time domain is clocked by a freerunning local clock configured to clock software operations.
 4. Themethod according to claim 1, wherein the at least one trigger timedomain comprises the first time domain, and the at least one periodictrigger event generated in the first time domain occurs in response to acondition being verified on a transition of at least one bit of acurrent timestamp value representing the instantaneous state of thefirst time domain, each bit of the current timestamp value beingcommunicated on a dedicated channel of a timestamp bus.
 5. The methodaccording to claim 1, wherein the at least one trigger time domain doesnot comprise the first time domain, each bit of the current timestampvalue representing the instantaneous state of the first time domainbeing communicated on a dedicated channel of a timestamp bus, and theacquiring the current timestamp value representing the instantaneousstate of the first time domain comprises loading a latch with bitspresent on each channel of the timestamp bus, the loading the latchbeing controlled at the instants of detecting the at least one periodictrigger event.
 6. The method according to claim 1, wherein the at leastone trigger time domain comprises the second time domain, and the atleast one periodic trigger event generated in the second time domain isdetected in response to a periodic signal being generated in the secondtime domain.
 7. A system comprising: a first device comprising a firstcounter configured to provide a current timestamp value representing aninstantaneous state of a first time domain; a second device comprising asecond counter configured to provide a current timestamp valuerepresenting an instantaneous state of a second time domain; and a thirddevice comprising: a local clock generator configured to clock a thirdtime domain; and a synchronization module configured to: detect at leastone periodic trigger event generated in at least one trigger time domainselected from the first time domain, the second time domain and thethird time domain; acquire, at instants of detection of the at leastperiodic one trigger event, the current timestamp values representingthe first time domain, the second time domain and the third time domain,other than the at least one trigger time domain; compare differentialdurations between current timestamp values that are respectivelyacquired successively; and generate a control configured to synchronizethe second time domain with the first time domain, based on thecomparison.
 8. The system according to claim 7, wherein thesynchronization module is configured to acquire the current timestampvalues at same instants of detecting a same periodic trigger event, orat different instants of detecting different periodic trigger events. 9.The system according to claim 7, wherein the first device comprises aperipheral component interconnect express “PCIe” interface configured todefine the first time domain by a precision time measurement “PTM”protocol, the second device comprises a network interface “Ethernet”configured to define the second time domain by a precision time protocol“PTP,” and the local clock generator of the third device is configuredto clock software operations.
 10. The system according to claim 7,wherein the at least one trigger time domain comprises the first timedomain, the first counter being configured to communicate each bit ofthe current timestamp value on a dedicated channel of a timestamp bus,and wherein the synchronization module is configured to detect the atleast one periodic trigger event generated in the first time domain inresponse to a condition being verified on a transition of at least onebit on the respective channel of the timestamp bus.
 11. The systemaccording to claim 7, wherein the at least one trigger time domain doesnot comprise the first time domain, the first counter being configuredto communicate each bit of the current timestamp value on a dedicatedchannel of a timestamp bus, and wherein the synchronization modulecomprises a latch on the timestamp bus and is configured to acquire thecurrent timestamp value representing the instantaneous state of thefirst time domain by controlling loading of the latch, at the instantsof the at least one periodic trigger event, with bits present on eachchannel of the timestamp bus.
 12. The system according to claim 7,wherein the at least one trigger time domain comprises the second timedomain, and the synchronization module is configured to detect the atleast one periodic trigger event generated in the second time domain, inresponse to a periodic signal being generated in the second time domain.13. A system on chip comprising: a peripheral component interconnectexpress “PCIe” device comprising a first counter configured to provide acurrent timestamp value representing an instantaneous state of a firsttime domain; an Ethernet device comprising a second counter configuredto provide a current timestamp value representing an instantaneous stateof a second time domain; and a central processing unit “CPU” devicecomprising: a local clock generator configured to clock a third timedomain; and a synchronization module configured to: detect at least oneperiodic trigger event generated in at least one trigger time domainselected from the first time domain, the second time domain and thethird time domain; acquire, at instants of detection of the at leastperiodic one trigger event, the current timestamp values representingthe first time domain, the second time domain and the third time domain,other than the at least one trigger time domain; compare differentialdurations between current timestamp values that are respectivelyacquired successively; and generate a control configured to synchronizethe second time domain with the first time domain, based on thecomparison.
 14. The system on chip according to claim 13, wherein thesynchronization module is configured to acquire the current timestampvalues at same instants of detecting a same periodic trigger event, orat different instants of detecting different periodic trigger events.15. The system on chip according to claim 13, wherein the PCIe devicecomprises a PCIe interface configured to define the first time domain bya precision time measurement “PTM” protocol, the Ethernet devicecomprises an Ethernet interface configured to define the second timedomain by a precision time protocol “PTP,” and the local clock generatorof the CPU device is configured to clock software operations.
 16. Thesystem on chip according to claim 13, wherein the at least one triggertime domain comprises the first time domain, the first counter beingconfigured to communicate each bit of the current timestamp value on adedicated channel of a timestamp bus, and wherein the synchronizationmodule is configured to detect the at least one periodic trigger eventgenerated in the first time domain in response to a condition beingverified on a transition of at least one bit on the respective channelof the timestamp bus.
 17. The system on chip according to claim 13,wherein the at least one trigger time domain does not comprise the firsttime domain, the first counter being configured to communicate each bitof the current timestamp value on a dedicated channel of a timestampbus, and wherein the synchronization module comprises a latch on thetimestamp bus and is configured to acquire the current timestamp valuerepresenting the instantaneous state of the first time domain bycontrolling loading of the latch, at the instants of the at least oneperiodic trigger event, with bits present on each channel of thetimestamp bus.
 18. The system on chip according to claim 13, wherein theat least one trigger time domain comprises the second time domain, andthe synchronization module is configured to detect the at least oneperiodic trigger event generated in the second time domain, in responseto a periodic signal being generated in the second time domain.
 19. Thesystem on chip according to claim 13, wherein the CPU device is amicroprocessor.
 20. The system on chip according to claim 13, whereinthe CPU device is a microcontroller.